In dynamic contrast imaging, a process in which a contrast medium administered to a subject flows into an organ or tissue to be diagnosed and flows out of the organ or tissue is imaged over plural time phases. Pixel values of medical images acquired by dynamic imaging over plural time phases reflect changes in a level of the contrast medium in the blood. A time density curve (TDC), which is a graphic plot of successive changes in the pixel values, allows a level of a tissue lesion, such as a degree of malignancy to be determined. Also, by analyzing the TDC, it is possible to learn a half life of the contrast medium in the blood, a blood flow rate, and a blood volume, and thereby qualitatively and quantitatively evaluate the blood flow. In this way, various diseases are diagnosed based on results of blood flow dynamics analysis conducted using medical images obtained by dynamic imaging. With such dynamic imaging, positional displacement occurs due to breathing of the subject during the imaging, posing a problem in conducting image analysis.
For example, dynamic imaging in a lung field involves holding breath a few times. The lungs are organs whose volumes change greatly with each breath. It is difficult for the subject to inflate the lungs in a same way each time imaging is performed. Because images are acquired by performing imaging by holding breath a few times, the volumes and shapes of the lungs in the acquired images may vary each time. In such a case, a conventional technique aligns plural images differing from one another in time phase and conducts blood flow dynamics analysis based on the aligned images using a time density curve.